73 research outputs found
Oxygen Absorption in Free-Standing Porous Silicon: A Structural, Optical and Kinetic Analysis
Porous silicon (PSi) is a nanostructured material possessing a huge surface area per unit volume. In consequence, the adsorption and diffusion of oxygen in PSi are particularly important phenomena and frequently cause significant changes in its properties. In this paper, we study the thermal oxidation of p+-type free-standing PSi fabricated by anodic electrochemical etching. These free-standing samples were characterized by nitrogen adsorption, thermogravimetry, atomic force microscopy and powder X-ray diffraction. The results show a structural phase transition from crystalline silicon to a combination of cristobalite and quartz, passing through amorphous silicon and amorphous silicon-oxide structures, when the thermal oxidation temperature increases from 400 to 900 °C. Moreover, we observe some evidence of a sinterization at 400 °C and an optimal oxygen-absorption temperature about 700 °C. Finally, the UV/Visible spectrophotometry reveals a red and a blue shift of the optical transmittance spectra for samples with oxidation temperatures lower and higher than 700 °C, respectively
Anisotropic distribution of orientations of crystalline domains in calcite bio-minerals revealed by high-resolution x-ray diffraction microscopy
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Evidence of pore correlation in porous silicon: An x-ray grazing-incidence study
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Reticulated nanostructures in calcareous biocrystals imaged by 3D ptychography
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